Clocks and Watches

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Clocks and Watches, devices used to measure or indicate the passage of time. A clock, which is larger than a watch, is usually intended to be kept in one place; a watch is designed to be carried or worn. Both types of timepieces require a source of power and a means of transmitting and controlling it, as well as indicators to register the lapse of time units.

In a clock, the source of power may be produced by weight, a mainspring, or an electric current. Except in electric or electronic clocks, periodic adjustments, such as lifting the weight or tightening the spring, are needed. The motive force generated by the power source in a mechanical clock is transmitted by a gear train and regulated by a pendulum or a balance wheel. In such a clock, the time may be reported audibly by the striking of a gong or chime and is registered visually by the rotation of wheels bearing numerals or by the position of hands on a dial. In electric or electronic clocks, time may be shown by a display of numbers.

A mechanical watch uses a coiled spring as its power source. As in spring-powered clocks, the watch conserves energy by means of a gear train, with a balance wheel regulating the motive force. In self-winding watches, the mainspring is tightened automatically by means of a weight on a rotor that responds to the arm movements of the wearer.

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